Electric fence



E. D. WILLIS ELECTRIC FENCE Filed Dec. 19, 1938 April 30, 1940.

ATTORNEY.

enema Apr. 30', 1940 i 2,198,715

UNITED STATES PATENT OFFICE Application 2 3? 246,595 4.:

This invention relates to electric fences, and ing when the circuit is closed and current is more particularly to a means for automatically flowing in the fence. v

' regulating and limiting the current which flows These objects are attained by means of a novel therein. apparatus for charging the fence including a 5 Electric fences, or in other words, fences of the thermionic device, preferably a conventional 5 type which are electrically charged in order to vacuum tube of the screen grid type, inserted in deliver a shock to an animal coming in contact series in the circuit whereby the current flowtherewith, are well known.- Previous to this inmg in the circuit must traverse the space in vention therehas been no way for maintaining the tube between the cathode and the anode a continuous current in such a fence which is thereof. The current is automatically controlled 10 safe, and at the same time capable of delivering by the variation in potential of a control eleca shock of sufficient magnitude to keep all sorts trode, or grid, to compensate for variations in of animals away from the fence. Most electric the external resistance of the entire circuit. fences have employed means for intermittently Inthe drawing the single figure is a wiring is making and breaking the circuit so as to shock diagram, using conventional symbols, which I an animal touching the fence but thereafter proshows the invention embodied in an electric vide a short interval in which to break away from fence having a single bare fence wire. supported thefence. on insulating posts.

It is well known that animals of different kinds Referring now in more detail to the drawing,

have different internal resistances, and the inthenumeral l0 indicates the primary coil of a 20 ternal resistance of the same animal mayvary transformer which is connected to -a suitable from time to time. Also, the resistance in the source of electric current, usually the standard circuit due to a good or a poor contact of the 110 volt 60 cy le household ppl The S con animal with the fence or ground may. vary widecry of the transformer is divided into two coils 1y. Because of these wide variationsin resist- II and I 2. Coil II has s'uihcient turns to supply 25 ance previous electric fences have been unsatisa voltage f ppr x m ly 300 v lts across the factory because if they are provided with sufllcoil when the primary voltage is 110 volts. The cient resistance to render them safe at all times, coil I2 has sufficient turns to deliver approxithe shock which is delivered to an an'iinal of mately 6.3 volts, and is connected directly to the relatively high resistancewill be so slightas to be cathode heater filament l3 of a thermionic 30 unnoticeable. 0n the other hand, if the revacuum tube ll. The tube I4 is aconventional sistance of the circuit is low enough sothat the radio tube of thev screen grid type. It has an current is high enough to deliver a shock to an anode IS, a grid I6, a cathode l8, and a screen animal of relatively high internal resistance, grid O terminal of e Se dary ccilll then the effect on an animal of low resistance of the transformer is connected to the anode I5 5 may be such as to stun or oven kill the animal. and the other terminal of the secondary coil is It is an object of this invention, therefore, to connected to the ground l9.

provide a circuit for an electric fence which is e ca hode l8 f the tube I4 is connected so arranged that a continuous current will flow through a resistance P fe y hav ng a re- 40 therein whenever an animal touches the fence, sistance Value of 1000 Ohms, a single bare Wire 40 but this current will be limited to a value that which confititutes the electrically charged can never become dangerous, no matter what portion of the fence, This wire 2| is supported the animals resistance may be. Another object on posts m ,the ground is insuiated is to provide an electric fence having an autotherefrom by suitable insulators T gnd maticany variable cumpensatmg impedance for is connected to the cathode l8, but with the re- 45 sistance 20 intermediate the cathodeand grid.

regulating the flow of current. Still another ob- The anode '5 is connected to th n J'ectis to provide a fence having means for deand this connectio i id sicreen livering current thereto including a thermionic n S-pmv ed Wm? Suitable;

resistance in order to impress a positive potenelectric discharge device. Another object. is to a1 on the screen grii In the-particular prolong the lifegof the thermionic device by bodiment disclosed herein this resistance con- D y a 011mm which is normally Open, and sists of a neon lamp 22 which is so connected which 1s cl sed nly wh m foreign object that when the circuit is closed this neon lamp touches the fence. Still another. object of the win glow and indicate that some object is in invention is the provision of means for indicatcontact with the fence and is touching the 55 ground. In place of the neon lamp any suitable resistance may be used, but of course, a simple resistance will not have the dual function of acting as a resistance and indicating the operation of the electric circuit.

A small condenser 23, preferably of 1 microfarad capacity, is connected to the ground wire and the cathode I8. The current delivered to The values of resistance, impedance and capacity of the various elements of the circuit are preferably chosen so that the maximum current which can flow in the circuit when the fence is short circuited by a connection having a negligible resistance is approximately 15 milliamperes. This current is insuihcient to be dangerous to any animal which may come in contact with the fence.

The operation of a vacuum tube of the type shown in this circuit is well known, and it is therefore believed to be unnecessary to go into its operation in detail. The operation of the entire circuit is as follows: with the switch in the line circuit closed the primary coil ll! of the transformer will be energized and will induce currents in the secondary coils I l and I2. Since the circuit including the secondary coil l2 and the heater l3 for the cathode is closed, the heater will be incandescent and will heat the cathode 18. The circuit, including the secondary coil II, the tube l4 and the fence is open until some foreign object, such as an animal, comes in contact with the fence.

' When the circuit is closed by any conductor placed between the fence and ground, a current will flow therein, crossing the space between the anode l5 and the cathode iii of the tube It. The maximum current which flows in the circuit is limited by When the circuit is closed by a conductor, cur-' rent flows across the space between the anode and cathode of the tube and through the two grids. l6 and H. The grid I6 is at a negative potential relative to the cathode because of the drop in potential across the resistance 20. Therefore, the

grid opposes the flow of current to a certain extent and limits it to the value stated.

Now, if an animal having a high resistance closes the circuit instead of the aforementioned conductor having no resistance, the current tends to drop. However, thistcauses a decrease in the I. R. drop across resistance 20, the grid l6 thereby becomes less negative, and the current flows more freely across. the space in the tube. Thus, the increase .in resistance of the circuit due to the animal is substantially compensated for by the decreased impedance of the tube It. No matter what the resistance closing the circuit happens to be, it is automatically compensated for by the change in impedance of the tube.

This circuit does not hold the current exactly constant for all values of the circuit resistance. However, it does regulate it within relatively close limits, of which the maximum current is safe to animal life, while the minimum current is capable of delivering a strong shock. With the circuit illustrated the current will vary between approximately 7 and 15 milliamperes where the resistance across the fence varies between 30,000 and 0 ohms respectively.

As stated above, the neon lamp acts as the necessary resistance to maintain the screen grid I I at a positive potential less than that of the anode. At the same time the neon lamp is not illuminated unless the circuit is closed, and therefore, the fact that the lamp glows indicates to the owner of the fence that some foreign object is in contact therewith; It will, of course, be obvious that instead of the neon lamp any suitable resistance may be substituted therefor. However, a simple resistance would not indicate the closed or opened condition of the circuit.

It will also be obvious that instead of connecting one terminal of the secondary coil l l of the transformer to the ground l9 it may be connected to a second bare wire supported on the posts 24 in spaced and insulated relation to the wire 2|.

The circuit herein shown and described makes it unnecessary to rectify the alternating current supplied from the line because the tube It is itself I a rectifier and supplies direct current to the fence.

This effect is, of course, produced by the tube It which is a vacuum tube of the uni-directional type. This feature renders the device very simple and economical to construct.

It will be apparent that this invention obviates difliculties present in former fences by maintaining a substantially constant current in the fence at all times, no matter what resistance may be placed across the fence. Furthermore, the current can never rise to a value that may cause death or an exceedingly severe shock to an animal which may come in contact therewith.

The scope of the invention is indicated in the appended claims:

1. An electric fence comprising a normally open electric circuit including a source of electric current, a bare fence wire and an automatically variable impedance, said impedance including a vacuum tube of the uni-directional type comprising an anode, a cathode, and a control electrode, a connection between said anode and the source of electric current, a connection between said cathode and said bare wire, a connection between said control electrode and said cathode, said last mentioned connection including a resistance, and a connection between said source of current and a conductor normally insulated from said bare fence wire.

2.1111 electric fence comprising a normally open electric circuit including a source of electric current, a bare fence wire and an automatically variable impedance in series therewith, said circuit being adapted to be closed by varied resistances, said impedance including a thermionic device having an anode, a cathode and a control electrode, a connection between said source of electric current and said anode, a connection between said cathode and said-fence wire, a connection between said control electrode and said cathode, said last named connection including a resistor element, a second control electrode in said thermionic device, and a connection includinga resistor element between said second control electrode and said anode.

3. An electric fence comprising a normally .open electric circuit including a bare fence wire and a source of electric current, a thermionic electric discharge device having an anode, a cathode, and a control electrode. a connection between said anode and the source of electric current, a connection between the cathode and said fence wire, a connection including an impedance between said cathode and said control electrode, and a connection between the source of current and the ground.

4:. An electric fence comprising a normally open electric circuit including ,a bare fence wire and a source of electric current, a thermionic electric discharge device having an anode, a cathode, a control electrode and a screen grid, a connection between said anode and said source of electric current, a connection between the anode and said screen grid, said last mentioned connection includinga resistor element, a connection between the cathode and said ience wire, a connection including an impedance between said 3 cathode and said control electrode, and a connection between the source of current and the ground.

5. The combination set forth in claim 4wherein the resistor element located between the anode and the screen grid is a neon lamp.

6. An electric fence comprising a. normally open electric circuit adapted to be closed by varied resistances and including an impedance in series therewith, said impedance including a thermionic electric discharge device having an anode, a cathode and a control electrode, said impedance being automatically variable to maintain the current flowing in the circuit, when closed,

within predetermined limits.

ELISWORTH D. WILLIS. 

